Biomass gasification/pyrolysis system and process

ABSTRACT

A system and process capable of promoting the energy content of a syngas produced from a biomass material. The system and process entail compacting a loose biomass material and simultaneously introducing the compacted biomass material into an entrance of a reactor tube, and then heating the compacted biomass material within the tube to a temperature at which organic molecules within the biomass material break down to form ash and a fuel gas mixture. The fuel gas mixture is withdrawn from the tube and the ash is removed from the tube through an exit thereof. The entrance and exit of the tube, the compaction step, and the removal step cooperate to inhibit ingress of air into the tube by forming a plug of the biomass material at the entrance of the tube and a plug of ash at the exit of the tube.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/270,393, filed Jul. 8, 2009, and is a continuation-in-part patentapplication of co-pending U.S. patent application Ser. No. 12/760,241,filed Apr. 14, 2010, which claims the benefit of U.S. ProvisionalApplication No. 61/212,624, filed Apr. 14, 2009. The contents of theseprior patent applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention generally relates to the conversion of organiclignocellulosic materials (biomass) into useful fuels (biofuels), andmore particularly to a system and process capable of continuousconversion of biomass into synthesis gas (syngas).

Syngas is a gas mixture containing carbon monoxide (CO) and hydrogen gas(H₂) produced by the conversion of carbonaceous materials, such as coal,petroleum, and biomass materials. Though having a lower energy densitythan natural gas, syngas is suitable for use as a fuel source for avariety of applications, including but not limited to gas turbines andautomotive internal combustion engines. Syngas can also be used toproduce methanol and hydrogen, or converted via the Fischer-Tropschprocess to produce a synthetic petroleum substitute.

The use of syngas as a fuel is more efficient than direct combustion ofthe original biomass because more of the energy contained in the biomassis extracted by the conversion process, known as gasification. Within atypical biomass gasifier, a carbonaceous material is combusted in anatmosphere where the oxygen content is below the stoichiometric limit atwhich complete combustion can occur. This oxygen-starved combustion ofcarbonaceous material releases volatiles, in the case of dry feedstock,produces a carbon-rich char, and releases heat. This heat raises thetemperature of non-combusted carbonaceous material, causing it topyrolyze, releasing flammable volatiles such as carbon monoxide (CO),hydrogen (H₂) and, depending on the temperatures used, may also producemethane (CH₄) and hydrocarbon molecules having a greater number ofcarbon atoms. This blend of flammable volatiles is termed synthesis gas,or syngas, for short.

In the case of dry feedstock material, it is possible to convert thechar into flammable volatiles. One such method is the injection of steam(H₂O), which reacts with the char to produce more CO and H₂, accordingto the reaction

C+H₂O→H₂+CO

Consequently, the biomass gasification process employssub-stoichiometric quantities of oxygen or air to combust a portion ofthe biomass and through pyrolysis, and the optional injection of steam,produce syngas and heat (energy).

Pyrolysis is an endothermic process, and various heating techniques havebeen proposed for use in the production of syngas, including but notlimited to partial combustion of the biomass products through airinjection, direct heat transfer by mixing with a hot gas, indirect heattransfer with exchange surfaces (for example, walls or tubes), anddirect heat transfer with circulating solids. Each of these heatingtechniques has significant technical shortcomings. For example, partialcombustion results in poor-quality products, for example, a syngashaving an energy content of 150 BTU/ft³ or less, because of the dilutionof the fuel gasses by the nitrogen in the injected air and the gaseousproducts of the combustion. With direct heat transfer, typically with aproduct gas that is reheated and recycled, a shortcoming is that a verylarge ratio of recycle gas to feed gas is required to provide sufficientheat with reasonable gas flowrates. For indirect heat transfer, it canbe difficult to maintain desired heat transfer rates because the processdeposits coatings on the heat transfer surfaces that act as insulatingmaterials. Finally, direct heat transfer with circulating solids iseffective but requires complex technology because the circulatingsolids, which typically transfer heat between a burner and a pyrolysisreactor, involve a moving bed that requires a significant investment inequipment and energy management to be effective in a continuous process.

Various types of gasifier designs are known, including counter-currentfixed bed (up-draft) gasifiers, con-current fixed bed (down-draft)gasifiers, fluidized bed gasifiers, and entrained flow gasifiers. Themost common type of gasifier used in biomass gasification is believed tobe the up-draft design, in which a gasification agent (air, oxygenand/or steam) flows upward through a permeable bed of biomass andcounter-currently to the flow of ash and other byproducts of thereaction. These gasifier designs have significant technicalshortcomings, particularly if the intent is to produce a syngas having ahigher energy content, for example, about 300 BTU/ft³ or more, fromcellulosic agricultural residue. Most current available technologies,including up-draft and down-draft fixed beds, fluidized beds, orentrained flow gasifiers, can be either pressurized or non-pressurized(atmospheric) design. As previously noted, the use of air for partialcombustion to provide the energy for pyrolysis and gasificationintroduces a large volume of inert diluting gas (nitrogen), which is themajor contributing factor to the production of low BTU syngas. Becausebiomass is a low-energy content fuel and is dispersed geographically,low-BTU syngas negatively affects the economic payback for the gasifiersystem. The use of an external heat source and/or pure oxygen wouldovercome the diluent effect of air to allow for the production of amedium BTU syngas (about 300 BTU/ft³ or more). However, a major problemremains as to how to prevent the ingress of air while allowing theegress of syngas from the feed material ingress and the egress of ashfrom the spent material outlet.

BRIEF DESCRIPTION OF INVENTION

The present invention provides a system and process capable of efficientproduction of syngas from biomass materials in a manner capable ofyielding energy contents of as much as 300 BTU/ft³ and higher.

According to a first aspect of the invention, the system includes areactor containing a reactor tube having an internal passage, anentrance to the internal passage, and an exit to the internal passage,means for compacting a loose biomass material and simultaneouslyintroducing the compacted biomass material into the entrance of thereactor tube, means for heating the compacted biomass material withinthe reactor tube to a temperature at which organic molecules within thecompacted biomass material break down to form ash and a fuel gas mixturecomprising predominantly carbon monoxide and hydrogen gases, means forwithdrawing the fuel gas mixture from the reactor tube, means forremoving the ash from the reactor tube through the exit thereof, andmeans comprising the entrance and the exit of the reactor tube, thecompacting means, and the removing means for inhibiting ingress of airinto the reactor tube by sufficiently compacting the biomass material atthe entrance of the reactor tube to form a plug of the compacted biomassmaterial at the entrance and compacting the ash at the exit of thereactor tube to form a plug of the ash at the exit.

According to a second aspect of the invention, the process includescompacting a loose biomass material and simultaneously introducing thecompacted biomass material into an entrance of a reactor tube, heatingthe compacted biomass material within the reactor tube to a temperatureat which organic molecules within the compacted biomass material breakdown to form ash and a fuel gas mixture, withdrawing the fuel gasmixture from the reactor tube, removing the ash from the reactor tubethrough an exit thereof, and inhibiting ingress of air into the reactortube by sufficiently compacting the biomass material at the entrance ofthe reactor tube to form a plug of the compacted biomass material at theentrance and compacting the ash at the exit of the reactor tube to forma plug of the ash at the exit.

By preventing the ingress of air with the biomass and ash plugs at theentrance and exit, respectively, of the reactor tube, the system andprocess are capable of producing a syngas having an energy contenthigher than otherwise possible. Other aspects and advantages of thisinvention will be better appreciated from the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a biomass gasifier system incorporating aneutral atmospheric pressure capability in accordance with a preferredaspect of this invention.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 schematically represents a biomass gasifier system 10 inaccordance with an embodiment of the invention. The system 10 isconfigured to have a neutral atmospheric pressure reactor 12, whoseconfiguration is capable of minimizing energy input and equipmentcomplexity of the system 10. FIG. 1 represents a biomass material asbeing delivered to the reactor 12 from a bulk hopper 16 via a feederdevice 18, represented in FIG. 1 as an auger powered by a motor (M),though other methods of delivery are also within the scope of theinvention, such as through the use of a ram or by gravity feed only. Thebiomass material enters a reactor tube 14 within the reactor 12 throughan entrance or throat 20 at an upper end of the tube 14. The tube 14serves as the containment vessel and defines an internal passage withinwhich the gasification process occurs, producing syngas as a desiredproduct and dry ash as a byproduct. The reactor 12 is configured suchthat syngas flows out, as does the ash. These characteristicsdistinguish the present invention from typical gasifiers. The reactor 12is represented as comprising a single reactor tube 14, though thereactor 12 could comprise an array of parallel tubes (linear, planar, orconvex surface) in accordance with co-pending U.S. patent applicationSer. No. 12/760,241. If an array of reactor tubes 14 is employed, thetubes 14 are preferably arranged so that their throats 20 lie on acommon two-dimensional (2-D) surface (either Euclidian or Riemann), suchas on a rectilinear grid or other geometric arrangement for couplingwith the biomass hopper 16. Though the reactor 12 and its tube 14 arerepresented in FIG. 1 as vertically oriented, the tube 14 can beoriented horizontally or at various angles with respect to each otherand with respect to gravity (vertical).

The biomass conveyed from the hopper 16 into the open throat 20 of thereactor tube 14 is preferably size-reduced, as is typically the case forcorn stover, wood chips, gin trash, dry distillers grain solids, andmess hall organic waste. The particle size of the biomass material ispreferably limited to about one-sixth of the diameter of the reactortube 14. For reasons discussed in more detail below, it is advantageousthat the amount of biomass material in the hopper 16 be maintained at asufficient level to ensure that there is always biomass available toevery tube 14 within the reactor 12, such that backflow of syngas isminimized. The biomass within the hopper 16 may be stirred to maintainthe material at a uniform height within the hopper 16, especially if theplane in which the tube throat 20 lies is substantially normal to theearth's surface. In FIG. 1, the vertical orientation of the reactor tube14 results in the biomass material being conveyed downward by gravityand/or other conveying means to the tube 14.

The exterior of the reactor 12 is represented in FIG. 1 as provided withheating elements 22 for heating the biomass within the tube 14. Theheating elements 22 can be of a variety of types, including but notlimited to resistance heaters, radiant heaters including heat lamps,plasma heaters and electromagnetic heaters. The heating elements 22 arepreferably arranged so that the tube 14, and particularly multipleaxially-spaced regions (Zones #1, #2 and #3) of the tube 14, capturesubstantially all of the heat energy generated by the elements 22 and,if multiple tubes 14 are present, the temperature within a given zonewithin a tube 14 is as similar as possible to the same zone within othertubes. The diameter of the reactor tube 14 is preferably selected suchthat the heating elements 22 are as nearly as possible able to uniformlyheat the biomass material across the cross-section of the tube 14 andwithin the time period required for the biomass material to travelthrough the tube 14 and become pyrolized. Thus, the length and diameterof the reactor tube 14 are interdependent based on this common concept.

FIG. 1 further shows the reactor 12 fitted with a gas line 24 thatwithdraws syngas from the tube 14 as it is produced. The entrance to thegas line 24 is preferably oriented and located outside the heated zonesto reduce the likelihood that biomass material will enter the gas line24. In the embodiment represented in FIG. 1, syngas produced by thepyrolysis and gasification process is drawn through the gas line 24 witha blower 26 (or other suitable device, such as a compressor). The blower26 draws the syngas through a series of heat exchangers (HX) andparticulate filters 30 before being delivered to a prime mover (asindicated in FIG. 1), a holding tank, downstream process, fuel cell, orany other suitable destination. A gasification agent may be employed toassist in the conversion of char to syngas via the known water-gas shiftreaction. As represented in FIG. 1, the gasification agent may be steamand the source of the steam may be water that is drawn from a watersource by a pump 42 and then heated by a heat exchanger 28 through whichthe syngas passes, such that the syngas serves as the heat source forgenerating the steam introduced into the tube 14 through the line 36.

According to a preferred aspect of the invention, the reactor 12 and itstube 14 are configured to promote compaction of the biomass within thethroat 20 of the tube 14, such that backflow of syngas through the tube14 is inhibited. For this purpose, the biomass is preferablycontinuously supplied to the tube 14 to form a moving “plug” of biomassmaterial within the tube throat 20. The throat 20 may be configured tohave a flared shape (not shown) that promotes compaction of the biomassas it enters the tube 14. The tube 14 may be optionally sealed toprevent backflow of syngases toward the tube throat 20, as well as toallow for maintenance. The continuous supply of biomass to the tube 14also serves to push the dry ash byproduct of the reaction through thetube 14 and into a manifold 32, which can employ gravity and/or anotherash removal system 34 (such as the auger represented in FIG. 1) toremove the ash from the system 10. In this manner, in addition toforming the aforementioned plug of biomass material to seal the throat20 of the tube 14, the biomass is continuously supplied to the reactortube 14 to promote the formation of an ash plug within the ash removalsystem 34 located downstream of the manifold 32, effectively forming aseal within the manifold 32. The formation of an ash plug within themanifold 32 can be promoted by tapering the manifold 32 as shown in FIG.1, which forces or compacts the ash similarly to an extrusion process.An alternative is to have a section of pipe where the transportmechanism (for example, the auger or other device) through the manifold32 is absent or interrupted and the ash is forced through this portion,thus compacting the ash slightly.

In addition to forming a barrier to the ingress of air into the tube 14,plugging the ends of the tube 14 with biomass and ash also serves tobetter contain the heat within the reactor tube 14 to promote thegasification reaction and reduce the risk of a fire in the hopper 16.The degree to which the tube throat 20 is tapered, the degree to whichthe feeder device 16 is capable of packing the biomass material into thethroat 20, and the distance of the feeder device 16 from the opening ofthe throat 20 will all affect the axial length and density of thebiomass plug within the tube 14. It can be appreciated that there may bemore than one combination of these three factors which provide thedesired or optimal performance in a given configuration. To address thecontingency that the tube 14 becomes starved of biomass material, thetube 14 may be equipped with means (not shown) for closing its throat22. Such closing means may include, but is not limited to, driving thecorresponding feeder device 16 further into the throat 20 of the starvedtube 14 and providing with a flat plate to promote a better seal,provide a knife valve at or near the throat 20 to seal a starved tube14, and/or closing a valve (not shown) through which syngas is drawnfrom the starved tube 14. Each of these closing means, individually orin combination, may be employed to minimize the risk of fire, minimizeback-diffusion of the desired syngas product, and minimize heat loss topromote process efficiency and reduced hazard risks.

Further features of the system 10 and of the tube 14 of the system 10are discussed below, some of which are similar to or derived fromcertain process and design parameters reported in U.S. patentapplication Ser. No. 12/357,788.

The temperature of pyrolysis employed by this invention can vary, butpreferably ranges from about 800 to about 1100° C. Within the reactortube 14, there is preferably a temperature profile which mosteffectively converts the solid biomass into syngas. This profile mayprompt the use of the three-zone heater arrangement shown in FIG. 1where, for example, biomass encounters the first heating zone (Zone #1)after it enters the tube 14 where the biomass is heated to nearly itsvolatilization temperature (typically around 350° C.), then enters asecond heating zone (Zone #2) where its temperature is increased to thefull pyrolysis temperature, such that molecules are rapidly crackedbefore they can form heavy or toxic compounds. If a third heating zone(Zone #3) is used as shown in FIG. 1, the temperature within the thirdzone is maintained so that mineral ash remaining after pyrolysis willnot form low-melting point glasses that may not flow readily through thereactor tube 14.

Waste heat generated from the heating elements 22 and lost from the tube14 may be harvested and used for a variety of purposes. The gas effluentmay also be run through a heat exchanger, heat pipe, or other means ofheat transfer to provide heat which can be used to advantage in theoverall method. The waste heat can be conveyed in many ways, includingbut not limited to a working fluid, a heat pipe (single-phase ortwo-phase), a conductive media such as metal or diamond, by radiation,or by convection of a suitable working fluid. The harvested waste heatmay be used, as nonlimiting examples, to dry incoming biomass, heat thereactor tube 14 (such as at Zone #1), and heat devices used to removeliquid and/or solid residues from the system. Waste heat may also beharvested in more useful forms, such as for the purpose of running aStirling engine for mechanical work, operating a thermoelectric cooler(Peltier effect) for electrical power, or used outside the system 10 foressentially any desired purpose. Waste heat, including exhaust gassesfrom a prime mover or SOFC, can be particularly useful for drying abiomass material that has a high moisture content. Injection of hot, dryair into the hopper 16 could be used for this purpose to obtain severalbenefits, including driving-off excess moisture in the biomass materialand separating or fluffing the biomass material to avoid bridging orrat-holing.

If the primary axis of the reactor tube 14 is horizontal, it may beadvantageous for the axis to tilt downward toward the end of the tube 14opposite its throat 20. The purpose of this slope is to encourage anygasses, rolling debris, or packed ash to be conveyed to the ash manifold32 coupled to the end of the tube 14. If the primary axis of the reactortube 14 is essentially vertical, it may be advantageous to provide thetube 14 with one or more spikes (not shown) that project into theinterior of the tube 14 so that biomass material falling into the tube14 impinges the spikes to break up any large biomass chunks as well asrestrict the flow of biomass material through the tube 14 and therebyincrease the residence time of the biomass material within the hottestzones of the tube 14. In addition, a grate (not shown) can be located ator near the base of each spike to assure that little or no biomassmaterial falls entirely through the reactor tube 14 without becominggasified.

As previously noted, to minimize energy input and equipment complexity,the system 10 of this invention is configured to have a neutralatmospheric pressure achieved by plugging the entrance (throat 20) andexit (manifold 32) of the tube 14 with biomass and ash, respectively.Such a capability can be promoted by utilizing highly sensitivedifferential pressure sensors 38 at the tube entrance and/or the ashremoval section of the system 10 and a closed-loop control system 40 tomonitor and adjust the volumetric rate of gaseous discharge via theblower 26 used to draw the syngas through the gas line 24. The integrityof the biomass and ash seals at a given pressure is a function ofleakage rate due to the porosity/composition of the biomass or ash plug.The porosity of the plugs can be adjusted by the degree of compaction ofthe biomass material being transported. This capability is particularlydesirable from the stand point of eliminating the need for a lock hoppersystem to prevent the ingress of air into the reactor tube 14 orunwanted leakage of syngas from the ash removal section 34 by ensuringthat the system 10 operates with inlet and outlet pressures withincertain limits.

The closed-loop control system 40, with suitable parameters (such as aPID controller or other methods known to those skilled in the art), canalso be used to introduce a controlled amount of water or water vapor(including steam) based on properties of the syngas. These propertiesmay include, but are not limited to, the moisture content of the syngas,the moisture content of the incoming carbonaceous feedstock material,the amount of liquid condensed out in a condenser, the conductivity ofthe gas, or other means known to those skilled in the art. There arealso means by which the output gas properties, such as pressure ortemperature, can be used in a chemical and/or mechanical system toregulate the amount of water introduced. Introduction of the water maybe accomplished in many ways, including but not limited to injection,osmosis, control valve, diffusion, or wicking/capillary action.

As should be understood, particularly in view of the foregoingdiscussion, the ingress of air into the reactor tube 14 would have anunwanted diluent effect on the syngas produced, thus reducing itsheating value and leading to an overall net energy efficiency decrease,while leakage of syngas from the reactor 12 would introduce potentiallysignificant safety issues and have a net overall decrease in energyefficiency, especially if the leakage is such as to reduce the energyproduction capabilities of the system 10. Without the use of biomass andash plugs within the tube throat 20 and manifold 32, respectively,direct diffusion of air into the system 10 and syngas out of the system10 at balanced is only 4.277×10⁻⁶ and 9.427×10⁻⁴ mass fraction of syngasproduction rate, respectively. By utilizing plugs at these locations,the direct diffusion rate is even smaller, resulting in an efficientsyngas production process capable of yielding energy contents of as muchas 300 BTU/ft³ and higher.

While the invention has been described in terms of a specificembodiment, it is apparent that other forms could be adopted by oneskilled in the art. For example, the physical configuration of thesystem 10 and its components could differ from that shown, and materialsand processes other than those noted could be used. Therefore, the scopeof the invention is to be limited only by the following claims.

1. A system for producing syngas from biomass materials, the systemcomprising: a reactor containing a reactor tube having an internalpassage, an entrance to the internal passage, and an exit to theinternal passage; means for compacting a loose biomass material andsimultaneously introducing the compacted biomass material into theentrance of the reactor tube; means for heating the compacted biomassmaterial within the reactor tube to a temperature at which organicmolecules within the compacted biomass material break down to form ashand a fuel gas mixture comprising carbon monoxide and hydrogen gases;means for withdrawing the fuel gas mixture from the reactor tube; meansfor removing the ash from the reactor tube through the exit thereof; andmeans comprising the compacting means, the entrance and the exit of thereactor tube, and the removing means for inhibiting ingress of air intothe reactor tube by sufficiently compacting the biomass material at theentrance of the reactor tube to form a plug of the compacted biomassmaterial at the entrance and compacting the ash at the exit of thereactor tube to form a plug of the ash at the exit.
 2. The systemaccording to claim 1, wherein the inhibiting means further comprises:means for monitoring pressures at the entrance and the exit of thereactor tube; and means for monitoring and adjusting a volumetric rateof the fuel gas mixture withdrawn from the reactor tube by thewithdrawing means based on the pressures at the entrance and the exit ofthe reactor tube.
 3. The system according to claim 1, wherein thereactor tube comprises first and second heating zones through which thebiomass material travels in sequence through the reactor tube, and thesecond heating zone is at a higher temperature than the first heatingzone.
 4. The system according to claim 1, further comprising means forinjecting a gasification agent into the reactor tube.
 5. The systemaccording to claim 4, wherein the gasification agent is steam.
 6. Thesystem according to claim 4, wherein the reactor tube comprises firstand second heating zones through which the biomass material travels insequence through the reactor tube, the second heating zone is at ahigher temperature than the first heating zone, and the gasificationagent is introduced into the second heating zone within the reactortube.
 7. The system according to claim 1, wherein the compacting meanscomprises a hopper containing a quantity of the biomass material.
 8. Thesystem according to claim 7, wherein the compacting means comprises anauger that transports the biomass material from the hopper to theentrance of the reactor tube.
 9. The system according to claim 1,wherein the entrance of the reactor tube is flared to promote compactionof the biomass material within the entrance.
 10. The system according toclaim 1, wherein the removing means comprises a manifold that tapers topromote compaction of the ash within the exit of the reactor tube.
 11. Aprocess of producing syngas from biomass materials and performed withthe system of claim 1, the process comprising: compacting the loosebiomass material and simultaneously introducing the compacted biomassmaterial into the entrance of the reactor tube; heating the compactedbiomass material within the reactor tube to a temperature at whichorganic molecules within the compacted biomass material break down toform the ash and the fuel gas mixture; withdrawing the fuel gas mixturefrom the reactor tube; removing the ash from the reactor tube throughthe exit thereof; and inhibiting ingress of air into the reactor tube bysufficiently compacting the biomass material at the entrance of thereactor tube to form the plug of the compacted biomass material at theentrance and compacting the ash at the exit of the reactor tube to formthe plug of the ash at the exit.
 12. A process of producing syngas frombiomass materials, the process comprising: compacting a loose biomassmaterial and simultaneously introducing the compacted biomass materialinto an entrance of a reactor tube; heating the compacted biomassmaterial within the reactor tube to a temperature at which organicmolecules within the compacted biomass material break down to form ashand a fuel gas mixture comprising carbon monoxide and hydrogen gases;withdrawing the carbon monoxide and hydrogen gases from the reactortube; removing the ash from the reactor tube through an exit thereof;and inhibiting ingress of air into the reactor tube by sufficientlycompacting the biomass material at the entrance of the reactor tube toform a plug of the compacted biomass material at the entrance andcompacting the ash at the exit of the reactor tube to form a plug of theash at the exit.
 13. The process according to claim 12, wherein theinhibiting step further comprises: monitoring pressures at the entranceand the exit of the reactor tube; and monitoring and adjusting avolumetric rate of the fuel gas mixture withdrawn from the reactor tubebased on the pressures at the entrance and the exit of the reactor tube.14. The process according to claim 12, wherein the biomass materialtravels in sequence through first and second heating zones within thereactor tube, and the second heating zone is at a higher temperaturethan the first heating zone.
 15. The process according to claim 12,further comprising injecting a gasification agent into the reactor tube.16. The process according to claim 15, wherein the gasification agent issteam.
 17. The process according to claim 15, wherein the biomassmaterial travels in sequence through first and second heating zoneswithin the reactor tube, the second heating zone is at a highertemperature than the first heating zone, and the gasification agent isintroduced into the second heating zone within the reactor tube.
 18. Theprocess according to claim 12, wherein the compacting step comprisestransporting the biomass material from a hopper to the entrance of thereactor tube.
 19. The process according to claim 12, wherein theentrance of the reactor tube is flared to promote compaction of thebiomass material within the entrance.
 20. The process according to claim12, wherein the ash removed from the reactor tube enters a manifold thatis tapered to promote compaction of the ash within the exit of thereactor tube.